After initially declining to discuss gun policy with the White House, representatives from Walmart met with Attorney General Eric Holder on Thursday as part of the Obama Administration’s ongoing talks on guns and gun control. Walmart’s apparent reluctance may reflect the extent to which gun sales have become an important part of the retailer’s bottom line. But just how important are they?

The U.S.’s largest retailer has what you might call an on-again, off-again relationship with guns. Back in 2006, Walmart stopped selling guns at a third of its stores, citing a lack of demand and “diminished customer relevancy.” Instead, it replaced firearms with other sporting goods like home fitness and exercise products. According to a 2006 New York Times article, this move coincided with Walmart’s shift away from rural areas and toward cities and suburbs.

But when the recession hit in 2009, even “everyday low prices” couldn’t keep sales from slumping. Walmart experienced seven straight quarters of same-store sales declines in the U.S., triggering the retailer to expand its product selection. Among the additions: fishing rods, craft and sewing supplies, and guns.

Selections of rifles, shotguns and ammunition previously sold at Walmart were back as the retailer tried once again to target customers in more rural parts of the country. Today, guns are sold at between 1,700 and 1,800 of the 4,000 outlets across the U.S., says Walmart spokesperson Kory Lundberg. At about a third of its stores, the offerings include “modern sporting rifles,” a term that refers to the type of semiautomatic rifle used in the shooting at Sandy Hook Elementary School in December.

Walmart doesn’t release specific gun-sales figures, so it’s difficult to determine what share of total U.S. gun sales are made at the country’s largest retailer. But given its broad, national reach, Walmart is likely the single biggest firearms seller in the U.S. And lately business has been good: even before reports that Walmart had sold out of semiautomatic rifles following Sandy Hook, chief merchandising officer Duncan MacNaughton said in October that revenue from gun sales increased 76% in the first half of the most recent fiscal year, while ammunition sales increased 30%.

The other significant gun seller in the U.S. is outdoor retailer Cabela’s. It doesn’t release gun-sales figures either, but hunting equipment in general, which includes firearms, made up 41% of the chain’s sales in 2011, according to Bloomberg News.

While Walmart may be concerned about a possible assault-weapons ban or other pieces of gun-control legislation from the Obama Administration, it’s possible that new gun laws could actually help the retailer. The Huffington Post is reporting that Vice President Joe Biden is likely to propose that independent gun dealers force buyers to go through Walmart’s certified background checks, which could end up driving more foot traffic into Walmart stores.